Redundant vehicle control systems

ABSTRACT

A redundant control system for a vehicle includes: one or more actuator housings; a plurality of actuator pistons coupled to the actuator housings, each of the actuator pistons mechanically coupled to one another and a common output device; a plurality of primary stages coupled to the actuator housings, each of the primary stages operatively coupled to move a respective actuator piston relative to at least one of the actuator housings, and each of the primary stages functioning independent of any other primary stage when the control system is operating in a flight-operation mode; and an auxiliary stage operatively coupled to move a first of the plurality of actuator pistons relative to at least one of the actuator housings when the control system is operating in a ground-operation mode, with each of the plurality of primary stages being responsive to movement of the first actuator piston by the auxiliary stage.

TECHNICAL FIELD

This specification generally relates to redundant vehicle controlsystems operable in one or more ground and flight operating modes.

BACKGROUND

Critical valve position sensors of a fly-by-wire main rotor actuatormust be tested for proper functioning prior to each flight to confirmthat a dormant failure has not occurred. The existence of a dormantfailure would pose an unacceptable safety risk. In conventional controlsystems, this requires that two or more redundant hydraulic stages eachhave their own auxiliary pressure source (e.g., one or more pumps) tomove the valves when commanded during pre-flight testing, and, in turn,change the output signal of the sensors. These hydraulic stages aretypically powered by a main system pump, and are therefore not operableduring pre-flight testing when the vehicle's primary hydraulic sourcesare dormant. Thus, the auxiliary pressure sources are added to thesystem solely to facilitate pre-flight testing, and are otherwise notused during flight.

SUMMARY

One aspect of the present disclosure provides a redundant control systemfor a vehicle operable in one or more ground-operation modes and one ormore flight-operation modes. The control system includes: one or moreactuator housings; a plurality of actuator pistons coupled to the one ormore actuator housings, each of the actuator pistons mechanicallycoupled to one another and a common output device; a plurality ofprimary stages coupled to the one or more actuator housings, each of theprimary stages operatively coupled to move a respective actuator pistonrelative to at least one of the one or more actuator housings, and eachof the primary stages functioning independent of any other primary stagewhen the control system is operating in a flight-operation mode; and anauxiliary stage operatively coupled to a first actuator piston of theplurality of actuator pistons to move the first actuator piston relativeto at least one of the one or more actuator housings when the controlsystem is operating in a ground-operation mode, with each of theplurality of primary stages being responsive to movement of the firstactuator piston by the auxiliary stage.

In some examples, the one or more actuator housings are coupled to astructural component of the vehicle, and the common output device iscoupled to a control surface of the vehicle.

In some examples, the one or more actuator housings include a firstactuator housing defining an interior cavity containing a hydraulicfluid, and at least one of the plurality of actuator pistons resides inthe interior cavity, such that movement of the at least one actuatorpiston includes translation through the interior cavity to displace atleast a portion of the hydraulic fluid.

In some examples, the plurality of actuator pistons are directlyconnected to a common output shaft, such that movement of one actuatorpiston effects movement of the other actuator pistons.

In some examples, one or more of the primary stages and the auxiliarystage include hydraulic stages including a pressure source.

In some examples, a primary stage from among the one or more of theprimary stages is coupled to a second actuator piston and includes aservo valve and a bypass valve, the bypass valve operatively coupled toregulate fluid communication between the servo valve and the secondactuator piston. In some examples, the bypass valve includes: a frame; aspring-biased spool coupled to move relative to the frame, the spooldefining an interior bore; a spring-biased plunger movable within theinterior bore of the spool; and a displacement sensor responsive tomovement of the plunger relative to the frame. In some examples, thebypass valve further includes a pilot valve operatively coupled to movethe spring-biased spool relative to the frame in response to movement ofthe first actuator piston by the auxiliary stage. In some examples, theframe includes an interior bore receiving a portion of the pilot valveas the pilot valve moves the spring-biased spool, and pressurization ofa portion of the interior bore inhibits operation of the pilot valve. Insome examples, when the control system is operating in aground-operation mode, the bypass valve is moved to a bypass positionwhere the servo valve is isolated from a pressure source. In someexamples, the control system further includes a spring biasing memberoperatively coupled to urge a portion the servo valve to a predeterminedtesting position when the servo valve is isolated from the pressuresource, and movement of the first actuator piston by the auxiliary stagecauses displacement of an internal portion of the servo valve. In someexamples, the control system further includes a sensor responsive todisplacement of the internal portion of the servo valve.

Another aspect provides a method of operating a redundant control systemof a vehicle including one or more actuator housings and a plurality ofactuator pistons coupled to the one or more actuator housings, each ofthe actuator pistons mechanically coupled to one another and a commonoutput device. The method includes: in a flight-operation mode of thecontrol system, driving a first actuator piston of the plurality ofactuator pistons to move relative to at least one of the one or moreactuator housings with a first primary stage of a plurality of primarystages, the first primary stage functioning independent of any otherprimary stage; and in a ground-operation mode of the control system,driving the first actuator piston to move relative to at least one ofthe one or more actuator housings with an auxiliary stage, driving abypass valve and a servo valve of a second primary stage to move inresponse to driving the first actuator piston to move, and detectingmovement of the bypass valve and the servo valve of the second primarystage.

In some examples, the method further includes, in the flight-operationmode, operating one or more other primary stages in a passive state.

In some examples, the first primary stage includes a bypass valve, andthe method further includes, in the flight-operation mode, actuating thebypass valve of the first primary stage to an active state, andactuating the bypass valve of the second primary stage to a bypassstate.

In some examples, the bypass valve includes a frame and a spring-biasedspool coupled to move relative to the frame; and driving the bypassvalve to move includes: routing fluid from the at least one housing to apilot valve of the bypass valve as the first actuator piston movesrelative to the at least one housing, the pilot valve operativelycoupled to move the spring-biased spool relative to the frame inresponse by hydraulic fluid pressure. In some examples, detectingmovement of the bypass valve includes detecting movement of a plungercoupled to the spool with a displacement sensor disposed in an interiorbore of the frame.

In some examples, the servo valve includes a first stage and a secondstage, and driving the servo valve to move includes: routing fluid fromthe at least one housing to the second stage of the servo valve, routingat least a portion of the fluid from the second stage of the servo valveto the first stage of the servo valve; and displacing a spring-biasedspool of the second stage of the servo valve with hydraulic fluidpressure from the fluid. In some examples, detecting movement of theservo valve includes detecting movement of the spring-biased spool witha displacement sensor.

One or more embodiments of the present disclosure may provide a controlsystem for a vehicle that is operable in a ground-operation mode tofacilitate testing of a plurality of redundant hydraulic stages using alesser number of auxiliary pressure sources. That is, the number ofauxiliary pressure sources is less than the number of hydraulic stages.In some embodiments, the vehicle control system includes a singleauxiliary pressure source that is operable to facilitate testing ofmultiple hydraulic stages. Reducing the number of auxiliary pressuresources improves the vehicle control system by decreasing both cost andweight.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating an exemplary dual tandem actuator.

FIG. 1B is a diagram illustrating an exemplary dual parallel actuator.

FIG. 2 is a plan view diagram illustrating an exemplary redundantvehicle control system.

FIGS. 3A-3C are progressive diagrams illustrating an exemplary operationof a bypass valve of a redundant vehicle control system.

One or more elements of the drawings may be exaggerated to better showthe features, process steps, and results. Like reference numbers anddesignations in the various drawings may indicate like elements.

DETAILED DESCRIPTION

FIG. 1A illustrates a first example hydraulic actuator 100 in accordancewith one or more embodiments of the present disclosure. In someembodiments, the hydraulic actuator 100 can be incorporated in a vehiclecontrol system (e.g., the vehicle control system 10 of FIG. 2). Forexample, the hydraulic actuator 100 may be incorporated in an aircraftflight control system, such as a fly-by-wire control system. In someembodiments, the vehicle control system is operable in one or moreground and flight operating modes, as described below.

As shown in FIG. 1A, the hydraulic actuator 100 includes an actuatorhousing 102 defining an interior cavity 104 separated into a first fluidchamber 106 a and a second fluid chamber 106 b by a dividing wall 108.In this example, the first and second chambers 106 a, 106 b are arrangedin an end-to-end configuration. The exterior of the housing 102 includesa coupling 110 for attaching the actuator 100 to a structural componentof a vehicle (e.g., a portion of the vehicle's frame). The hydraulicactuator 100 further includes a first actuator piston 112 a and a secondactuator piston 112 b residing in the respective first and second fluidchambers 106 a, 106 b. The first and second actuator pistons 112 a, 112b are disposed on a common output shaft 114 extending through theinterior cavity 104 of the actuator housing 102. A distal end of theoutput shaft 114 includes a coupling 116 for attaching the actuator 100to a control surface of the vehicle.

The first and second actuator pistons 112 a, 112 b are driven to movethrough the actuator housing 102 by respective first and second primarystages 118 a, 118 b (shown schematically). The first and second primarystages 118 a, 118 b are designed to provide fluid pressure on eitherside of the corresponding first and second actuator pistons 112 a, 112 bto control movement of the pistons. Higher fluid pressure at one end ofthe chamber urges the piston towards the other end of the chamber.Movement of the first and second actuator pistons 112 a, 112 b effectsmovement of the output shaft 114, and therefore movement of the vehiclecontrol surface (not shown). Each of the first and second primary stages118 a, 118 b may include a hydraulic pressure system animated by apressure source including one or more pumps. The first and secondprimary stages 118 a, 118 b may be configured to function entirelyindependent of one another when the vehicle control system is operatingin a flight-operation mode. The independently functioning stages providea redundancy for the vehicle control system, such that failure of onestage does not render the control system inoperable. In some examples,one of the first and second primary stages 118 a, 118 b is operated in aneutral bypass mode while the other primary stage is operated in anactive mode during vehicle operations, such that only one of the primarystages is controlling the output shaft 114 at any given time.

FIG. 1B illustrates a second example hydraulic actuator 100′ inaccordance with one or more embodiments of the present disclosure.Similar to the example of FIG. 1A, the hydraulic actuator 100′ may beincorporated in a redundant vehicle control system operable in one ormore ground-operation modes and one or more flight-operation modes. Inthis example, the hydraulic actuator 100′ includes an actuator housing102′ defining an interior cavity 104′ separated into a first fluidchamber 106 a′ and a second fluid chamber 106 b′ by a dividing wall108′. In this example, the first and second chambers 106 a′,106 b′ arearranged in a side-by-side configuration. The exterior of the housing102′ includes a coupling 110′ for attaching the actuator 100′ to astructural component of a vehicle. The hydraulic actuator 100′ furtherincludes a first actuator piston 112 a′ and a second actuator piston 112b′ residing in the respective first and second fluid chambers 106 a′,106b′. In this example, the first actuator piston 112 a′ is coupled to afirst output shaft 114 a′ and the second actuator piston 112 b′ iscoupled to a second output shaft 114 b′. The distal ends of the firstand second output shafts 114 a′,114 b′ are linked by a coupling 116′.The coupling 116′ is also designed for attaching the actuator 100′ to acontrol surface of the vehicle. As in the example of FIG. 1A, the firstand second actuator pistons 112 a′,112 b′ are driven to move through theactuator housing 102′ by first and second primary stages 118 a′,118 b′,which may function independently when the vehicle control system isoperating in a flight-operation mode.

FIG. 2 illustrates a redundant vehicle control system 10 in accordancewith one or more embodiments of the present disclosure. The vehiclecontrol system 10 is operable in one or more ground-operation modes andone or more flight-operation modes. In some examples, the vehiclecontrol system 10 operates in a flight-operation mode when the vehicleis in an active state (e.g., powered on and in use). As noted above, asuitable vehicle control system may include two or more redundantprimary stages functioning independent of one another during aflight-operation mode, with only one of the primary stages operating inan active state at any given time. In some examples, the vehicle controlsystem 10 operates in a ground-operation mode when the vehicle is adormant state (e.g., powered off and not in use). Note that the vehiclecontrol system 10 is depicted in FIG. 2 in a ground-operation mode. Aground-operation mode may include a testing mode (e.g., a pre-flighttest mode), where one or more components of the vehicle control system10 are artificially stimulated and monitored to ensure properfunctioning. In the example described below, the primary stages of thevehicle control system 10 are stimulated and monitored during thetesting mode.

As shown in FIG. 2, the vehicle control system 10 includes an actuator200 (similar to the example described above with reference to FIG. 1A)and an auxiliary stage 500. The actuator 200 includes first and secondactuator pistons 212 a, 212 b driven through first and second fluidchambers 206 a, 206 b of an actuator housing 202 by a first primarystage 218 a (shown schematically) and a second primary stage 218 b(shown diagrammatically), respectively. The actuator 200 furtherincludes a displacement sensor 220 (e.g., a linear variable differentialtransformer or “LVDT”) for monitoring movement of the output shaft 214.Each of the first and second fluid chambers 206 a, 206 b includes a pairof fluid ports 222 a, 222 b and 224 a, 224 b at opposing ends of therespective chambers. As noted above, the first and second primary stages218 a, 218 b are designed to provide fluid pressure on either side(i.e., the “C1” or “C2” side) of the corresponding actuator pistons 212a, 212 b to control movement of the pistons, when the vehicle controlsystem 10 is operating in an flight-operation mode. Higher fluidpressure at one end of the chamber urges the piston towards the oppositeend. Thus, the primary stages are designed to move the pistons, andtherefore the output shaft, towards one end of the chamber(s) byinjecting hydraulic working fluid through the port located at theopposite end.

The second primary stage 218 b includes a pressure source 226 and returnreservoir 228. The pressure source 226 may include one or more suitablepressure regulating apparatuses (e.g. a pump) for controlling (e.g.,increasing) the pressure of a working fluid (e.g., a hydraulic fluid).The return reservoir 228 may include one or more vessels for receivingworking fluid passed through various components of the second primarystage 218 b, containing the working fluid, and supplying the workingfluid to the pressure source 226. The second primary stage 218 b furtherincludes a bypass valve 300 and a servo valve 400. When the vehiclecontrol system 10 is in a flight-operation mode, the servo valve 400receives pressurized working fluid from the pressure source 226 andconveys at least a portion of the pressurized fluid to the ports 224 a,224 b of the actuator 200 for driving the actuator piston 212 b. Thebypass valve 300 is disposed between the servo valve 400 and theactuator 200, and regulates fluid communication between these and othercomponents of the second primary stage 218 b. For example, as describedbelow, the bypass valve 300 may be movable between an active positionand a bypass position to regulate fluid communication between variouscomponents of the second primary stage 218 b.

A solenoid 230 is provided to control the bypass valve 300, as discussedbelow. In this example, the solenoid 230 includes a supply pressure port232 leading to the pressure source 226, a return port 234 leading to thereturn reservoir 228, and a bypass control port 236 leading to thebypass valve 300. As shown schematically in FIG. 2, the solenoid 230 isoperable in a first state (state A) and a second state (state B). Instate A, the return port 234 is blocked and the supply pressure port 232is in fluid communication with bypass control port 236, such thatpressurized working fluid is routed to the bypass valve 300. In state B,the supply pressure port 232 blocked and the return port 234 is in fluidcommunication with the bypass control port 236, such working fluid isrouted from the bypass valve 300.

FIGS. 3A-3C illustrate a bypass valve 300 (e.g., the bypass valveincorporated in the vehicle control system 10) in accordance with one ormore embodiments of the present disclosure. As shown, the bypass valve300 includes a frame 302 defining a central bore 303 in which a spool304 is disposed. The spool 304 is movable within the central bore 303 ofthe frame 302, and biased against a flange 305 of the frame 302 by aspring member 306. The spool 304 also defines a central bore 307 inwhich a plunger 308 is disposed. The plunger 308 is movable within thecentral bore 307. The central bore 307 of the spool 304 includes a firstspring chamber 309 a housing a first spring member 310 a and a secondspring chamber 309 b housing a second spring member 310 b. While each ofthe first and second spring chambers 309 a, 309 b are fluidicallyisolated from one another, both of the first and second spring chambers309 a, 309 b include fluid ports 313 open to the frame's central bore303, which allows working fluid passing through certain ports of theframe 302 (discussed below) to independently pressurize the respectivefirst and second spring chambers 309 a, 309 b. The first and secondspring members 310 a, 310 b counter bias the plunger 308, such that theplunger 308 is suspended by equal spring force in the central bore 307of the spool 304. Thus, the plunger 308 is moved through the spool'scentral bore 307 by the fluid pressure differential between the firstand second spring chambers 309 a, 309 b. The plunger 308 includes anarmature 311 projecting outward into the central bore 303 of the frame302. A displacement sensor 312 (e.g., an LVDT) disposed on the frame 302is responsive to movement of the armature 311 through the frame 302. Thedisplacement sensor 312 detects movement of both the plunger 308 and thespool 304, because the armature 311 is coupled to both of thesecomponents.

The outer surface of the spool 304 defines a plurality of alternatinglands 314 and grooves 315. The lands 314 sealingly engage the innersurface of the frame's central bore 303, such that the grooves 315 arefluidically isolated from one another. The outer surface of the frameincludes a plurality of ports 316-336 that receive and/or eject fluid toand/or from various other components of the primary stage (e.g., thesecond primary stage 218 b of FIG. 2). Fluid flow through the bypassvalve 300 is permitted when any two ports are aligned with the samegroove 315 of the spool 304. Fluid flow through the bypass valve 300 isinhibited when one of the lands 314 blocks a port or when only one portis aligned with a groove 315.

In this example, the plurality of ports includes a primary C1 chamberport 316 and a corresponding C1 servo valve port 318. The primary C1chamber port 316 leads to (or is otherwise in fluid communication with)the C1 side of an actuator fluid chamber (e.g., the fluid chamber 206 bof FIG. 2); and the port 318 leads to the servo valve (e.g., the servovalve 400 of FIG. 2). The ports 316,318 are positionally aligned on theframe 302, such that, in this example, they are always associated withthe same groove 315 in any position of the spool 304 (e.g., the spoolpositions shown in FIGS. 3A-3C). Notably, the fluid ports 313 of thefirst spring chamber 309 a are also always aligned with the ports316,318, in this example—meaning that the first spring chamber 309 aremains exposed to the C1 side of the actuator fluid chamber throughoutoperation of the bypass valve 300. The plurality of ports furtherincludes an auxiliary C1 chamber port 320, which also leads to the C1side of the actuator fluid chamber.

The plurality of ports still further includes a primary C2 chamber port322 and a corresponding C2 servo valve port 324. The primary C2 chamberport 322 leads to the C2 side of the actuator fluid chamber; and theport 324 leads to the servo valve. The ports 322,324 are positionallyclose, but offset on the frame 302, such that they may be associatedwith the same groove 315 or land 314 (in some examples) in only certainpositions of the spool 304 (e.g., the spool position shown in FIG. 3A).Notably, the fluid ports 313 of the second spring chamber 309 a are alsoalways aligned with the port 322, in this example—meaning that thesecond spring chamber 309 b remains exposed to the C2 side of theactuator fluid chamber throughout operation of the bypass valve 300. Theplurality of ports still further includes an auxiliary C2 chamber port326, which also leads to the C2 side of the actuator fluid chamber. Theports 320,326 are positionally close, but offset on the frame 302, suchthat they may be associated with the same groove 315 or land (in someexamples) in only certain positions of the spool 304 (e.g., the spoolpositions shown in FIGS. 3B and 3C).

The plurality of ports still further includes a main supply pressureport 328 and a servo valve pressure port 330. The main supply pressureport 328 leads to the main pressure source of the primary stage (e.g.,pressure source 226 of FIG. 2); and the servo valve pressure port 330leads to the servo valve. The ports 328,330 are positionally close, butoffset on the frame 302, such that they may be associated with the samegroove 315 or land 314 (in some examples) in only certain positions ofthe spool 304 (e.g., the spool position shown in FIG. 3A). The pluralityof ports still further includes a return reservoir port 332 and a C2chamber return port 334, which also leads to the C2 side of the actuatorfluid chamber. The return reservoir port 332 leads to a return reservoirof the primary stage (e.g., the return reservoir 228 of FIG. 2). Theports 332,334 are positionally close, but offset on the frame 302, suchthat they may be associated with the same groove 315 or land 314 (insome examples) in only certain positions of the spool 304 (e.g., thespool positions shown in FIGS. 3B and 3C). In this example, the ports332,334 may be aligned with the spool groove 315 that contains thebiasing spring member 306 biasing the spool 304 against the frame 302.The presence of the spring member 306 in the groove 315 creates aviscous drag force that causes significant pressure loss as fluid flowsfrom the C2 chamber return port 334 to the return reservoir port 332. Asdiscussed below, this pressure loss causes back pressure in the fluidlines that is used to animate other components of the primary stage. Theplurality of ports still further includes a control solenoid port 336,which leads to a control solenoid valve of the primary stage (e.g., thecontrol solenoid 230 of FIG. 2).

A pilot valve 338 is configured to effect movement of the spool 304within the central bore 303 of the frame 302, when the vehicle controlsystem is in a ground-operation mode. In this example, the pilot valve338 includes a valve chamber 340, a valve inlet port 342 and a stem 344.The valve inlet port 342 leads to the C1 side of the actuator fluidchamber. Working fluid received from the actuator fluid chamber entersthe valve chamber 340 and urges the stem 344 outward into the centralbore 303 of the frame 302 and towards a surface 345 of the spool 304(see FIG. 3C).

FIGS. 3A-3C illustrate the bypass valve 300 in three different operatingpositions (or “modes”). FIG. 3A illustrates the bypass valve 300 in anactive position; FIG. 3B illustrates the bypass valve 300 in a firstbypass position; and FIG. 3C illustrates the bypass valve 300 in asecond bypass position. Referring first to FIG. 3A, when the bypassvalve 300 is in the active position, pressurized working fluid isreceived through the control solenoid port 336, which urges the spool304 downward against the spring member 306 (note that “downward” refersto the axial direction towards the displacement sensor 312, and “upward”refers to the axial direction towards the pilot valve 338). Thehydraulic pressure force overcomes the spring force to drive the spool304 downward through the frame's central bore 303. In this position,first, the primary C1 chamber port 316 and the corresponding C1 servovalve port 318 are aligned with a spool groove 315, which allows fluidflow through the bypass valve 300 between the C1 side of the actuatorfluid chamber and the servo valve. Second, the primary C2 chamber port322 and the corresponding C2 servo valve port 324 are also aligned witha spool groove 315, which allows fluid flow through the bypass valve 300between the C2 side of the actuator fluid chamber and the servo valve.Third, the main supply pressure port 328 and the servo valve pressureport 330 are also aligned with a spool groove 315, which allows fluidflow through the bypass valve 300 between the main pressure source ofthe primary stage and the servo valve. As described in detail below,when the vehicle control system is in a flight-operation mode and thebypass valve 300 is in an active position, the servo valve receivespressurized working fluid from the main pressure source and distributesat least a portion of the fluid to one of the respective C1 and C2 sidesof the actuator fluid chamber to control movement of the valve piston.In this example, all other ports of the frame 302 are blocked by one ofthe spool's lands 314 or are not aligned in a groove 315 with any otherport.

Referring next to FIG. 3B, when the bypass valve 300 is in the bypassposition, pressurized working fluid is removed from the frame's centralbore 303 through control solenoid port 336. The lack of hydraulicpressure allows the spring member 306 to drive the spool back upwardtowards the top of the frame 302. In this position, first, the primaryC1 chamber port 316 and the corresponding C1 servo valve port 318 remainaligned with a common spool groove 315 to permit fluid flow through thebypass valve 300 between the C1 side of the actuator fluid chamber andthe servo valve. Second, the auxiliary C1 chamber port 320 and theauxiliary C2 chamber port 326 are also aligned with a spool groove 315,which allows fluid flow through the bypass valve 300 between the C1 andC2 sides of the actuator fluid chamber. Third, the return reservoir port332 and the C2 chamber return port 334 are also aligned with a spoolgroove 315, which allows fluid flow through the bypass valve 300 betweenthe C2 side of the actuator fluid chamber and the return reservoir ofthe primary stage. Thus, the C1 side of the actuator is in fluidcommunication with the C2 side of the actuator and the return reservoirof the primary stage. In this example, all other ports of the frame 302are blocked by one of the spool's lands 314 or are not aligned in agroove 315 with any other port. Notably, in this position, the servovalve pressure port 330 is blocked by a land 314, meaning that the servovalve is isolated from the supply pressure source, and therefore cannotdrive the valve piston, which places the primary stage in a “dormant” or“passive” state. As described in detail below, when the vehicle controlsystem is in a flight-operation mode or a ground-operation mode and thebypass valve 300 is in a bypass position, fluid flow through the primarystage is dictated by movement of the actuator shaft by one or more ofthe other redundant primary stages of the system. In particular, whenthe actuator shaft is driven toward the C1 side of the actuator, fluidflows out of the actuator and into the bypass valve 300, where a firstportion of the fluid is routed back to the C2 side of the actuator and asecond portion of the fluid is routed to the return reservoir via the C2chamber return port 334. Pressure loss accrued as fluid flows from theC2 chamber return port 334 to the return reservoir port 332 causes backpressure to build in the line leading to the C1 side of the actuator.The back pressure causes a third portion of the working fluid to flow tothe servo valve via the C2 servo valve port and a fourth portion of thefluid to flow to the pilot valve 338.

As shown in FIG. 3C, pressurized fluid received at the inlet port 342 ofthe pilot valve 338 causes the valve stem 344 to bear against thesurface 345 of the spool 304. The stem 344 presses the spool 304downward against the spring member 306 to drive the spool 304 partiallythrough the frame's central bore 303. Notably, the stroke of the pilotvalve 338 is not long enough to place the bypass valve 300 back into anactive position (see FIG. 3A). However, the spool displacement issufficient to allow the displacement sensor 312 to perceive movement ofthe armature 311.

Referring back to FIG. 2, the servo valve 400 includes a first stage forreceiving pressurized working fluid from the pressure source 226 andregulating the state of a second stage of the servo valve 400 usingfluid pressure. The second stage is for routing working fluid from thepressure source 226 to and from the C1 or C2 side of the actuator fluidchamber 206 b. The second stage of the servo valve 400 includes a frame(not shown) and a spool 402 movably supported within the frame. Thespool 402 is biased against the frame by a spring member 404. Adisplacement sensor 406 (e.g., an LVDT sensor) is responsive to movementof the spool 402 within the frame. Similar to the bypass valve 300, thespool 402 includes a plurality of lands and grooves that facilitate therouting of fluid between various ports of the frame. In this example,the frame includes a pressure inlet port 408, a return port 410, a C1chamber port 412, and a C2 chamber port 414. The pressure inlet port 408leads to the servo valve pressure port 330 of the bypass valve 300. Thereturn port 410 leads to the return reservoir 228. The C1 chamber port412 leads to the C1 servo valve port 318 of the bypass valve 300. The C2chamber port 414 leads to the C2 servo valve port 324 of the bypassvalve 300. As illustrated schematically in FIG. 2, the spool 402 ismovable within the frame between three different states—namely, statesA, B and C. In state A, the C1 chamber port 412 is in fluidcommunication with the pressure inlet port 408, and the C2 chamber port414 is in fluid communication with the return port 410. In state B, allof the ports are blocked by the lands of the spool 402 and/or misalignedwithin the grooves of the spool 402, such that there is no fluidcommunication between any of the ports. In state C, the C1 chamber port412 is in fluid communication with the return port 410, and the C2chamber port 414 is in fluid communication with the pressure inlet port408.

When the bypass valve 300 is in the active position (see FIG. 3A), thesecond stage of the servo valve 400 routes fluid to and from theactuator fluid chamber 206 b through the bypass valve 300. Morespecifically, when the servo valve 400 is in state A, working fluid isrouted to the C1 side of the chamber 206 b and routed from the C2 sideof the chamber 206 b; in state C, working fluid is routed to the C2 sideof the chamber 206 b and routed from the C1 side of the chamber 206 b;and in state B, there is no fluid flow between the servo valve 400 andthe chamber 206 b. In some examples, the volume of fluid routed to andfrom the actuator fluid chamber 206 b varies with the position of thespool 402 within the frame.

The first stage of the servo valve 400 includes a filter 416, a jet pipe418, a pair of opposing jet receivers 420, and a pair of opposing jetreceiver ports 422. As noted above, the first stage of the servo valve400 is designed to receive pressurized working fluid from the pressuresource 226 and regulate the state of a second stage of the servo valve400 using fluid pressure. When the vehicle control system 10 is in aflight-operation mode and the bypass valve 300 is in an active position,working fluid from the pressure source 226 is received (via the bypassvalve 300) at the filter 416 and subsequently routed to the jetreceivers 420 and the jet receiver ports 422. The volume of fluid thatpasses the respective jet receivers is regulated by the position of thejet pipe 418. The jet pipe 418 is responsive to an electronic controlsignal (not shown). The volume of fluid routed to the respective jetreceiver ports 422 dictates the position of the spool 402 within theframe—and therefor the state of the spool 402. When the bypass valve 300is the bypass position (see FIGS. 3B and 3C), the servo valve 400 isisolated from the pressure source 226, and the biasing force of thespring member 404 urges the spool 402 to state A.

As previously discussed, the vehicle control system 10 is also operablein one or more ground-operation modes. In some examples, the vehiclecontrol system 10 is operated in a ground-operation mode to test one ormore components of the primary stages 218 a, 218 b while the vehicle isdormant and not in use. In particular, the actuator 200, the bypassvalve 300, and the servo valve 400 can be tested by animating the secondprimary stage 218 b and detecting movement of the these components viatheir respective displacement sensors 220,312,406. In a ground-operationmode, the pressure source 226 may be rendered inoperable, because one ormore pumps included therein are not powered by the vehicle. As such, theauxiliary stage 500 is used to animate both of the primary stages 218 a,218 b for testing while the vehicle's primary hydraulic sources aredormant. In some examples, the auxiliary stage 500 includes one or morepumps or other pressure boosting devices, and is operable to animate thecomponents of the first primary stage 218 a, such that the firstactuator piston 212 a is driven towards the C1 side of the first fluidchamber 206 a. The first primary stage 218 a may include one or moredisplacement sensors to monitor movement of various components as theyhydraulically drive the first actuator piston 212 a. Because the firstand second actuator pistons 212 a, 212 b are coupled to a common outputshaft 214, movement of the first actuator piston 212 a results inidentical movement of the second actuator piston 212 b through thesecond fluid chamber 206 b. This movement of the second actuator piston212 b towards the C1 side of the second fluid chamber 206 b causes fluidto flow out of the second fluid chamber 206 b via fluid port 224 b andinto the bypass valve 300, which is in the bypass position.

As previously discussed in detail with reference to FIGS. 3B and 3C,when the bypass valve 300 is in the bypass position, a portion of theworking fluid received from the C1 side of the second fluid chamber 206b causes the pilot valve 338 to move the spool 304 downward through thecentral bore of the frame 302. This displacement of the spool 304 isdetected by the displacement sensor 312. As was also previouslydiscussed, another portion of the working fluid received from the C1side of the second fluid chamber 206 b is routed to the servo valve 400via the C1 servo valve port 318. The fluid is received at the C2 chamberport 412, with the spool 402 urged to the state A position by the springmember 404. Fluid received at the C2 chamber port is routed backwardsthrough the supply pressure lines to the first stage of the servo valve400. The fluid is fed through the filter 416 and routed by the jetreceivers 420 to the jet receiver ports 422, which causes the spool 402to move within the frame of the servo valve 400. The displacement sensor406 detects this movement of the spool 402.

The use of terminology such as “upward” and “downward” throughout thespecification and claims is for describing the relative positions ofvarious components of the system and other elements described herein.Unless otherwise stated explicitly, the use of such terminology does notimply a particular position or orientation of the system or anycomponent relative to the direction of the Earth gravitational force, orthe Earth ground surface, or other particular position or orientationthat the system or any components may be placed in during operation,manufacturing, and transportation.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the inventions.

What is claimed is:
 1. A redundant control system for a vehicle, thecontrol system operable in one or more ground-operation modes and one ormore flight-operation modes, and comprising: one or more actuatorhousings; a plurality of actuator pistons coupled to the one or moreactuator housings, each of the actuator pistons mechanically coupled toone another and a common output device; a plurality of primary stagescoupled to the one or more actuator housings, each of the primary stagesoperatively coupled to move a respective actuator piston relative to atleast one of the one or more actuator housings, and each of the primarystages functioning independent of any other primary stage when thecontrol system is operating in a flight-operation mode; and an auxiliarystage operatively coupled to a first actuator piston of the plurality ofactuator pistons to move the first actuator piston relative to at leastone of the one or more actuator housings when the control system isoperating in a ground-operation mode, with each of the plurality ofprimary stages being responsive to movement of the first actuator pistonby the auxiliary stage.
 2. The control system of claim 1, wherein theone or more actuator housings are coupled to a structural component ofthe vehicle, and wherein the common output device is coupled to acontrol surface of the vehicle.
 3. The control system of claim 1,wherein the one or more actuator housings comprise a first actuatorhousing defining an interior cavity containing a hydraulic fluid, andwherein at least one of the plurality of actuator pistons resides in theinterior cavity, such that movement of the at least one actuator pistoncomprises translation through the interior cavity to displace at least aportion of the hydraulic fluid.
 4. The control system of claim 1,wherein the plurality of actuator pistons are directly connected to acommon output shaft, such that movement of one actuator piston effectsmovement of the other actuator pistons.
 5. The control system of claim1, wherein one or more of the primary stages and the auxiliary stagecomprise hydraulic stages including a pressure source.
 6. The controlsystem of claim 1, wherein a primary stage from among the one or more ofthe primary stages is coupled to a second actuator piston and comprisesa servo valve and a bypass valve, the bypass valve operatively coupledto regulate fluid communication between the servo valve and the secondactuator piston.
 7. The control system of claim 6, wherein the bypassvalve comprises: a frame; a spring-biased spool coupled to move relativeto the frame, the spool defining an interior bore; a spring-biasedplunger movable within the interior bore of the spool; and adisplacement sensor responsive to movement of the plunger relative tothe frame.
 8. The control system of claim 7, wherein the bypass valvefurther comprises a pilot valve operatively coupled to move thespring-biased spool relative to the frame in response to movement of thefirst actuator piston by the auxiliary stage.
 9. The control system ofclaim 8, wherein the frame comprises an interior bore receiving aportion of the pilot valve as the pilot valve moves the spring-biasedspool, and wherein pressurization of a portion of the interior boreinhibits operation of the pilot valve.
 10. The control system of claim6, wherein, when the control system is operating in a ground-operationmode, the bypass valve is moved to a bypass position where the servovalve is isolated from a pressure source.
 11. The control system ofclaim 10, further comprising a spring biasing member operatively coupledto urge a portion the servo valve to a predetermined testing positionwhen the servo valve is isolated from the pressure source, and whereinmovement of the first actuator piston by the auxiliary stage causesdisplacement of an internal portion of the servo valve.
 12. The controlsystem of claim 11, further comprising a sensor responsive todisplacement of the internal portion of the servo valve.
 13. A method ofoperating a redundant control system of a vehicle, the control systemcomprising one or more actuator housings and a plurality of actuatorpistons coupled to the one or more actuator housings, each of theactuator pistons mechanically coupled to one another and a common outputdevice, the method comprising: in a flight-operation mode of the controlsystem, driving a first actuator piston of the plurality of actuatorpistons to move relative to at least one of the one or more actuatorhousings with a first primary stage of a plurality of primary stages,the first primary stage functioning independent of any other primarystage; and in a ground-operation mode of the control system, driving thefirst actuator piston to move relative to at least one of the one ormore actuator housings with an auxiliary stage; driving a bypass valveand a servo valve of a second primary stage to move in response todriving the first actuator piston to move; and detecting movement of thebypass valve and the servo valve of the second primary stage.
 14. Themethod of claim 13, further comprising, in the flight-operation mode,operating one or more other primary stages in a passive state.
 15. Themethod of claim 13, wherein the first primary stage comprises a bypassvalve, and further comprising, in the flight-operation mode, actuatingthe bypass valve of the first primary stage to an active state; andactuating the bypass valve of the second primary stage to a bypassstate.
 16. The method of claim 13, wherein the bypass valve includes aframe and a spring-biased spool coupled to move relative to the frame;and wherein driving the bypass valve to move comprises: routing fluidfrom the at least one housing to a pilot valve of the bypass valve asthe first actuator piston moves relative to the at least one housing,the pilot valve operatively coupled to move the spring-biased spoolrelative to the frame in response by hydraulic fluid pressure.
 17. Themethod of claim 16, wherein detecting movement of the bypass valvecomprises detecting movement of a plunger coupled to the spool with adisplacement sensor disposed in an interior bore of the frame.
 18. Themethod of claim 13, wherein the servo valve includes a first stage and asecond stage, and wherein driving the servo valve to move comprises:routing fluid from the at least one housing to the second stage of theservo valve; routing at least a portion of the fluid from the secondstage of the servo valve to the first stage of the servo valve; anddisplacing a spring-biased spool of the second stage of the servo valvewith hydraulic fluid pressure from the fluid.
 19. The method of claim18, wherein detecting movement of the servo valve comprises detectingmovement of the spring-biased spool with a displacement sensor.